In the production of di(4-aminocyclohexyl)methane by the catalytic hydrogenation of di(4-aminophenyl)methane, essentially three stereoisomers are formed. ##STR1##
It is known in the art that in order to produce a corresponding isocyanate (via the known phosgenation process) which is liquid and storage stable at room temperature (i.e. from 20.degree. to 25.degree. C.), the mixture of amine stereoisomers used for phosgenation must contain the trans,trans stereoisomer in relatively narrow amounts (typically from 15 to 40% by weight, and preferably from 18.5 to 23.5% by weight).
Numerous techniques are known in the art for the production of amine mixtures containing the requisite amount of the trans,trans isomer. Typical of these known techniques are those described in U.S. Pat. Nos. 3,153,088; 3,155,724; 3,393,236; 3,644,522; 3,711,550 and 3,766,272. These known techniques generally require the separation of an amine mixture containing the requisite amount of the trans,trans isomer from an amine mixture formed after hydrogenation and containing around 50% by weight of the trans,trans isomer. Processes are known in the art for the production of a di(4-aminocyclohexyl)methane mixture containing the requisite amount of the trans,trans isomer directly from di(4-aminophenyl)methane without the need for an intermediate separation step (see e.g. U.S. Pat. No. 2,606,928); however, the rates of reaction are much too slow for commercial application.
Numerous processes are known in the art for the production of di(4-aminocyclohexyl)methane from di(4-aminophenyl)methane via catalytic hydrogenation using supported and unsupported ruthenium catalysts. Typical of these processes are those disclosed in U.S. Pat. Nos. 2,494,563; 2,606,924; 2,606,928; 2,606,925; 3,347,917; 3,644,522; 3,676,495; 3,959,374; 3,743,677; 3,914,307; 3,825,586; and 4,161,492. While some of these processes yield an amine mixture containing the trans,trans isomer in an amount necessary to allow for the production of an isocyanate which is liquid and storage stable at room temperature, the rates of reaction are much too slow for commercial use.
Ruthenium based catalysts have also been described as being useful in the hydrogenation of (a) polycycloaromatic polyamines formed from aniline and formaldehyde (see U.S. Pat. No. 4,226,737); (b) 2,4-bis(p-aminobenzyl) aniline (see U.S. Pat. No. 3,557,180); (c) 2,4'-diaminodiphenylmethane (see U.S. Pat. No. 3,590,002); (d) tolylene diamine/formaldehyde condensates (see U.S. Pat. Nos. 3,330,850 and 3,361,814); and (e) di(4-nitrophenyl) methane (see U.S. Pat. No. 3,742,049). However, none of these processes relate to the present problem, i.e., production of a di-(4-aminocyclohexyl)methane containing from 15 to 40% by weight of the trans,trans isomer.
Recently, processes have been developed for the direct hydrogenation of di(4-aminophenyl)methane to produce a liquid mixture of the stereoisomers of di(4-aminocyclohexyl) methane via utilization of a supported rhodium catalyst (U.S. application Ser. No. 269,199, filed June 1, 1981), an unsupported ruthenium dioxide catalyst (U.S. application Ser. No. 268,979, filed June 1, 1981), and a supported ruthenium catalyst (U.S. application Ser. No. 269,200, filed June 1, 1981). Although the resultant amine mixture is liquid and contains the requisite amount of trans,trans isomer, the economics of those processes are not commercially acceptable primarily due to low yield (i.e., less than 95%) because of by-product formation and due to short catalyst life.
Finally, it is known that the formation of tars, decomposition products and/or condensation products formed during the hydrogenation of di(4-aminophenyl)methane can be reduced and that such hydrogenation be seen repeatedly without catalyst rejuvenation, if the catalyst used is a supported ruthenium catalyst which has been alkali-moderated (see, e.g. U.S. Pat. Nos. 3,636,108 and 3,697,449). The materials described as being useful for such alkali-moderation are all very basic compounds and include basic alkali metal compounds such as (1) the hydroxides, carbonates, bicarbonates, methoxides, ethoxides, propoxides, t-butoxides, and other alkoxides of lithium, cesium, rubidium, sodium and potassium and (2) sodamide. Specific alkali materials described in the working examples of the two noted patents are sodium methoxide, sodium propoxide, potassium t-butoxide, lithium methoxide, sodamide, potassium hydroxide, sodium hydroxide, potassium methoxide, sodium ethoxide, sodium bicarbonate, cesium hydroxide, and rubidium hydroxide. Finally, the use of such alkali-moderated ruthenium catalysts to produce a material having a relatively high trans,trans content is also known (see U.S. Pat. No. 3,711,550).